Spacer

ABSTRACT

A spacer in the form of an elongated, rectangular parallelepiped for use between the two glass plates of a gel cassette to delimit a space for receiving an electrophoresis gel between the glass plates where the spacer is made of glass.

This application is a national stage application of PCT/SE95/00762 filedJun. 21, 1995 published as WO95/35496 Dec. 28, 1995.

TECHNICAL FIELD

The invention relates to a spacer in the form of an elongated,rectangular parallelepiped for use between the two glass plates of a gelcassette to delimit a space for receiving an electrophoresis gel betweenthe glass plates, an arrangement at a gel cassette having two glassplates which are kept apart by means of at least two spacers to define aspace for receiving an electrophoresis gel, said spacers being in theform of elongated, rectangular parallelepipeds, and use of such a gelcassette.

BACKGROUND OF THE INVENTION

From U.S. Pat. No. 4,675,095 such a spacer is known in anelectrophoresis apparatus of the fluorescence detection type, wherelight from an excitation light source is projected from the side intothe electrophoresis gel to enable detection of fluorophor labelledfragments in samples that migrate along electrophoretic paths in thegel. From this U.S. patent it is apparent that the spacer is to betransparent with respect to the excitation light. In a commercialembodiment, this spacer is a plastic spacer. A disadvantage of a plasticspacer is that it is very difficult to produce the optical surfaces thatare necessary in order to project the excitation light into the gel withhigh efficiency. Moreover, tensions in the plastic material can giverise to unwanted optical effects. Furthermore, the useful life of suchspacers will be very short since the plastic material is easilyscratched. Another disadvantage is that the separation medium used isnot polymerized homogeneously enough adjacent to plastic spacers uponcasting, which causes so called "smiling" and a skew migration of thesamples in the gel during an electrophoresis run. Also, a poorlypolymerized gel can cause refractions that deflect the excitation light.

An attempt to eliminate these problems is known from WO 87/07719, wherethe spacers are divided and separate light guides are inserted betweenthe respective spacer parts to guide the excitation light into and outof the gel. In a commercial embodiment the spacer parts are of plasticwhile the light guides are of glass.

However, the handling of divided spacers of plastic with separate lightguides is problematic in view of the fact that a number of separateparts are to be fitted together. The light guides can namely easily endup misaligned and, moreover, sealing problems can appear upon casting ofthe gel.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to bring about a spacer of the typementioned in the introductory portion, which does not possess thedisadvantages of the spacers known so far.

This is attained by means of the spacer according to the invention inthat it is of glass.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an end view of a gel cassette having spacers in accordancewith the present invention.

PREFERRED EMBODIMENT

The single figure (FIG. 1) is an end view of a gel cassette having twoglass plates 1 and 2, which are kept separate by means of two spacers 3aand 3b according to the invention to delimit, in a manner known per se,a space 4 for receiving an electrophoresis gel (not shown).

The spacers 3a and 3b comprise separate, elongated, rectangularparallelepipeds and, in accordance with the invention, in the gelcassette shown, at least one of the spacers is completely made of glass,e.g. a boron silicate glass, in order for the gel cassette to be usablein electrophoresis apparatuses where excitation light is projected fromthe side into the gel for automatic direct detection of e.g. fluorephorlabelled samples.

By making the spacers 3a and 3b completely of glass a more homogenouspolymerization of a gel which is cast in the space 4 between the plates1 and 2, is obtained in that it polymerizes better against glass thanagainst plastic. In an electrophoresis run this will appear in the formof considerably less so called "smiling" and skew migration of thesamples in the gel adjacent to the edges.

Also, in case denaturated gels with urea are used, the improvedpolymerization causes the amount of urea that normally exits from thegel around the spacers to decrease.

Moreover, glass is more resistant to scratching than plastic.

Relative to the spacers according to the abovementioned WO 87/07719, thespacer according to the present invention also has the advantage that itcomprises a single piece which is to be applied between the glass plates1 and 2 without any need of fitting-in a light guide in the form of apiece of glass between a pair of pieces of plastic.

To improve the projection of excitation light from the side into the gelthrough the spacer of glass in accordance with the invention, at least aportion of the lateral surfaces of the spacer is polished.

The thickness of the spacers 3a and 3b can be selected to between 0.05and 1.0 mm in view of the thickness of between 0.25 and 0.55 mm ofelectrophoresis gels used today for automatic nucleic acid sequencing.

In order for the glass to be of necessary strength, e.g. upon removal ofthe gel from the glass plates 1 and 2 after an electorphoresis run, thespacer according to the invention is preferably made of hardened glass.

It is not possible with today's technique to thermally harden glass witha thickness of between 0.05 and 1.0 mm. Instead, the spacers accordingto the invention are chemically hardened.

Chemical hardening of glass is normally carried out in that the glasspieces are lowered into a special salt bath in which an ion exchangetakes place between the glass and the salt bath. Sodium in the glass isreplaced by potassium or any other substance having larger atoms.Hereby, a compressive stress is built up in the surface layer of theglass, which is the desired effect. The chemical hardening process lastsbetween a few hours and a few days.

Thus, by means of the invention the problems with so far known spacersin gel cassettes for automatic sequencing, have been eliminated.

I claim:
 1. An arrangement of a gel cassette, comprising:two glassplates; and at least two spacers disposed between said glass plates,wherein said spacers are arranged such that the thickness of the spacersdefines a space for receiving an electrophoresis gel, said spacers beingin the form of elongated, rectangular parallelepipeds, wherein at leastone of the spacers is made of glass, and wherein a portion of thelateral surfaces of at least one spacer is polished.
 2. An arrangementof a gel cassette, comprising:two glass plates; and at least two spacersdisposed between said glass plates, wherein said spacers are arrangedsuch that the thickness of the spacers defines a space for receiving anelectrophoresis gel, said spacers being in the form of elongated,rectangular parallelepipeds, and wherein at least one spacer ischemically hardened glass.
 3. An arrangement according to claim 1 or 2,wherein the thickness of the spacer is between 0.05 and 1.0 mm.
 4. Amethod for the detection of fluorophor labelled samples in a gel filledelectrophoresis apparatus, comprising:projecting an excitation lightinto a gel contained in said space in said arrangement of claim 1 or 2from the side of said electrophoresis apparatus; and detecting thefluorophor labelled samples directly.
 5. A method for the detection offluorophor labelled samples in a gel filled electrophoresis apparatus,comprising:projecting an excitation light into a gel contained in saidspace in said arrangement of claim 1 or 2 from the side of saidelectrophoresis apparatus; and detecting the fluorophor labelled samplesdirectly, wherein the thickness of the spacer is between 0.05 and 1.0mm.